I have a number of potential issues or maybe just questions around the install and operation of a rebuilt 4100. Something's not right and I need some guidance. I spent hours last night reading posts here and Googling but didn't find exactly what I need.

Engine is a late 60's 390 with a C6 auto in good shape with a purported rebuild of about 10-15K miles on it. I picked up a nice condition Autolite 4100 and rebuilt it. Original tag states "C5AF AV" and below that in smaller font: "A 5AC" The base is stamped 1.12. It has the auto choke and auto tranny kickdown.

Truck has been sitting for 4 years so I drained the gas, primed the oil and added 5 fresh gallons. Started up on the second try!! But it won't idle and wants to die unless I feather the gas until it warms up. Also has a bog when accelerating up past 1200 RPM. I've been checking for vacuum leaks but none so far found.

I have a number of questions and ideas. but one of the areas I believe I need to correctly adjust is the float level, and here is where I can't get a clear answer or clear explanation of the correct procedures. What is the correct float level? My Sorensen rebuild kit actually had multiple values and the one that looked best had different primary and secondary values. I tried setting it "dry" by the upside down check with the cardboard supplied gauge. Good news is that it is not overflowing so needles and floats seem to be working correctly. However, how do you do a more accurate wet setting? Appears to be two methods - one is the float setting and the other is the fuel depth. One good thread seems to state that both wet floats should be at 11/16". An engine builder locally said they should both be about level/parallel. Autozone says the primary should be 20/32" and the secondary should be 1 1/16". My rear wet float is almost level and it measures about 15/32". NONE of the data I've been able to find agree on the right setting nor do they explain in detail the correct way to measure using the wet float method.

I've got more questions like the choke settings and the vacuum port for hot air intake (currently open) and only getting 14 inches vacuum (I believe it should be 18 inches) etc., but I'd like to get the floats right before tackling them.

THANKS!!!!!!!!!!!!!!
David

 

FYI

C5AF-AV = C5AZ-9510-Y .. 4V 4100 Carburetor (Motorcraft CA-689-A)

Original application: 1965 Galaxie/LTD 390 (except Police Cruiser).

The same basic 4100 carb was used from 1958 thru 1969.

C2SZ-9A586-D .. Carburetor Tune Up Kit (Motorcraft CT-191-D)

B8AZ-9590-H .. Carburetor Master Overhaul Kit (Motorcraft CR-269)

The Motorcraft/Auto-Lite part numbers are the same.

Ford sold Auto-Lite, then started Motorcraft, transfering all the Auto-Lite part numbers over to Motorcraft part numbers.

 

Hi Bill - thanks for the numbers look up!! You don't happen to have quick access to the float level settings do you? (I put a rebuild kit in it but not a Motocraft brand)

David

 

Sorry, no..the settings are in the shop manual, not the parts catalog.

I can give you every part number for every part used in the carb, but that's about it.

 

Recheck the timing. It sounds slow.

 

Jimmy - once I got it warmed up she would idle. At 670 RPM and advance line plugged I set the timing to 8*. But still have bog going past 1200 rpm and once the truck cools and I start it back up - same problems - won't idle high, wants to die and I have to feather the throttle until it warms up.....


I just set the floats to be equal to each other at around 16/32"

Thanks!

 

Sounds like it is running lean. Also try putting the timing at 10*.
I also assume that you are using ported vacuum for the advance and not manifold vacuum.

 

MAYBE a little progress (though for today it's 2 steps back and 1/2 step forward): I also have an exhaust manifold leak and spent a few hours busting knuckles replacing the exhaust gasket (redid the adapter gasket yesterday) with a nice Felpro, and, no luck - still leaks, loud brap-brap-brap. My guess is the flange on the header is warped (should I try doubling up the exhaust gaskets or is that just a waste of time?).

Set the floats to about 16/32" and fired her up. Same behavior - bad/won't idle until warm, hesitations/bog, etc) At the end I was thinking about vacuum leak sources (sprayed starter fluid and no change around carb) and for the fun of it I decided to remove the vacuum hose to the power booster. Truck died almost instantly. Then I plugged the port and restarted, and it started right up and revved very smoothly!?!? Could I have a bad power booster? Is it suppose to hold vacuum? I hooked up my handheld mityvac to the power brakes booster hose and there is absolutely no vacuum that it will hold. Is this a bad booster??

Thanks again,
David

 

As original: Ford did not install exhaust manifold gaskets (to the head) on any FE engine except for HiPo 406/427's.

Only the thin metal heat shields were installed. These are right/left specific.

Power brake booster vacuum leak...it could be caused by this:

There's a power booster plastic check valve that the vacuum line attaches to. It fits into the outside of the booster using a rubber grommet.

The grommet could be bad, or the check valve itself.

 

I put a new PB-Booster (PBB) hose onto the plastic check valve, hookedup my hand vac to it and put my finger over the check valve end and it held some vacuum but fairly rapidly lost the vacuum - sounds like the valve is bad? But, when I insert it into the PBB grommet then it holds zero vacuum. This is a donor PBB off an old '73 parts truck so I don't know the condition of it.

I'm going to start the truck up (so a cold start) here shortly to see if it now starts and smoothly holds the high rpms with choke on as normal without it dying out.

Bill - since this has aftermarket long headers I'll assume the gasket is necessary. Is it a waste of my time to try 2 gaskets or should I just buy/find new exhaust manifolds/headers?

Thanks.

 

It'll be a heck of a lot cheaper to double gasket the manifolds rather then buy new headers.

Use some crocus cloth or 600 sandpaper to clean up both surfaces.

Check with your local parts store, someone might sell thicker gaskets.

 

Well, the double exhaust gaskets helped but still leaking a little. Unfortunately I started the truck up first time today (cold) and it still did not want to run/high idle properly and I had to feather it to keep it running. However with the PBB port plugged it did still run smoother and it was able to idle by itself sooner. I'm going to pick up a new PBB. I may give up and get an Edelbrock 1406 and see if that makes everything work

Thanks again.

 

Update: Purchased/installed new PBB - no more vacuum leaks there and brakes feel like power brakes now! There goes another $80 Still, the idle issue on cold start exists so I tried an Edelbrock 1406 carb and no problems on cold startup! Don't know if I got rid of a carb-spacer-gasket vacuum leak or there was something up with the Autolite 4100. There goes some more $$$!

Next issue - the Previous Owner rigged up some funky stuff for the braided SS accelerator cable and the cable adapter attaches to the carb. Well, to make it hold so it doesn't pivot when you step on it you really needed to crank on the carb nut on that corner - not a good thing. I tried cobbling a different bracket but it's not stable. So, I need an original FE accelerator cable bracket and tube/etc (from a 352 or 390) - can anyone help here??????

Thanks!
David
Fuquay Varina, NC